Homework Help:
Electrical Energy Problem

If someone could help me start this problem, it would be greatly appreciated.

Charges of equal magnitude 1.00X10^-15 C and opposite sign are distributed over the inner and outer surfaces of the cell wall. Find the force on the potassium ion (K+) if the ion is, (a) 2.70 micro-meters from the center of the cell, (b) 2.92 micro-meters from the center, and (c) 4.00 micro-meters from the center.